Method of producing secondary electron emitting cathodes



April 27, 1943.- .1. G'RUCH 2,317,754,

METHOD OF PRODUCING SECONDARY ELECTRO'N EMITTINGrV CATHODES Filed July 31, 1941 INVENTOR. lu! Gr/z'c/z ATTORNEYS' Patented Apr. 27, 1943 METHOD F PRODUCING SECONDARY l ELECTRON EMITTING CATHODES Paul Grlich, Dresden, Germany; vested in the Alien Property Custodian Application July 31, 1941, Serial No. 404,811 In Germany July 31, 1940 s claims. (Cl. o-27.5)

The invention relates to improvementsl in a method of producingsecondary electron emitting cathodes.

It is known that metals whose surface is covered with layers of earth alkali metals belongingto emitting cathodes is therefore of extremely great importance, particularly in the case of secondary electron multipliers, in which a number of secr ondary electron emitting electrodes are arranged one after another. f

It is an object .of the invention to produce secondary electron emitting cathodes and particularly to provide the same with an exterior metal layer of a thickness producing the best results.

Another object of the invention is to apply the metallic layer to the electrode body in a special apparatus and prior to the assemblage of the various cathodes in the tube in such a manner, that during `the period the metal is precipitated by vaporisation or during two successive periods of precipitation respectively, the layers under construction are being bombarded with primary electrons for testing the sensitiveness of the layers. The precipitation by evaporisation is interrupted when the maximum sensitiveness has been reached. In this manner, the surface of each electrode may be provided separately with a metallic layer, but it is also possible to give the apparatus such a construction that at the same time a plurality of electrodes are provided on their surface with the respective metal layer.

When the secondary electron emitting layers are produced in the manner just described it is hardly avoidable that the secondary electron emitting electrodes during their assemblage in the multiplier tube come in touch with the air, particularly with the oxygen contained in the same. The possible oxidation of the surface layer is a disadvantage insofar as it influences the energy necessary to produce the electron emission, which energy has to be increased considerably when the metallic layer on the electrode becomes oxidized. It is therefore another object of the present invention to counteract or compensate any oxidation of the metallic surface layer on the electrodes. After the various electrodes have been installed in the multiplier tube, they are subjected to a glow discharge, preferably in the presence of a rare gas or another chemically inactive gas. Such a glow discharge be tween the electrodes reduces any oxide which might have been formed and thus any loss in sensitiveness will have been regained. The glow discharge has the additional advantage that it liberates any adsorbed or absorbed gases and thereby makes the electrodes independent of the uncontrollable action of such gases.

Preferably, the glow discharge is maintained a sufcient length of time until the oxide layer formed during the period the electrodes were subjected tothe influence of the air is entirely reduced. The necessary operating conditions under which the glowdischarge is practiced, particularly the required` length of time, can easily be determined by tests.v However, it is also possible to measure in predetermined periods of time the sensitiveness by means of primary electrons as mentioned previously.

The method according to the invention is employed with a device shown in the drawing. 'I'he drawing however only shows an example of the device according to the invention.

Figure 1 illustrates the manufacture of the surface metal layer of thel secondary electron emitting electrodes. In bulb l the secondary electron emitting electrodes 3, 4, 5, 6 are attached to a support 2. The metal vwhich is to be preoipitated by vaporization, for instance an alkali metal, is fixed to the heated filament 1. After a certain time of vaporization thevaporization will be stopped in order to measure the secondary electron current. To this effect there is a potential of 120 volts 0n the one side between the heated filament 'l and the secondary electron emitting electrodes and a potential of volts on the other side between the secondary emitting electrodes 3, 4, 5, 6 and the end of the auxiliary electrode 8.

As soon as the secondary electron emitting electrodes 3, 4, 5, 6 havevreached the maximum sensitivity they will be assembled in the multiplier tube 9 as shown in Figure 2. The assemblage of secondary electron layersv in a multiplier tube is not limited to the example shown in Figure 2. In the multiplier tube 9 part l0 represents the light sensitive cathode which'is illuminated by the light falling in in the direction of the arrows. No. 11 shows an anode in form of a grid, having also the faculties of emitting secondary electrons. After having passed the grid Il these electrons strike (one after the other) the secondary electron emitting layers 3, 4, 5, 6 causing on their way the emission of more and more secondary electrons and nally strike the electrode l2 and at last give away their energy to anode I3.

In the above described example the manufacturing method according to the invention was shown having 4 secondary electron emitting electrodes. In the same way it will be possible to manufacture less or more than 4 secondary elec-a` tron emitting electrodes. y

What I claim is:

1. A method for producing secondary electron emitting electrodes comprising precipitating a thin surface layer of an alkali metal on a metal base prior to the installation of the electrodes in an electron multiplier, installing the-electrodes having said thin layer thereon in said electron multiplier, and then subjecting the electrodes to a glow-discharge until. any oxidation of said thin layer has been reduced.v A 2. A method for producing secondary electron emitting electrodes comprising precipitating a thin surface layer of an alkali metal on a metal base priorto the installation of the electrodes in an electron multiplier, continuously controlling the thickness of the precipitated layer by measuring the sensitiveness of the secondary electron emission until the maximum sensitiveness is obtained, installing the electrodes having said thin layer thereon in said electron multiplier, and then subj ecting the electrodes to a glow discharge until any oxidation of said thin layer has been reduced. Y

A method for producing secondary electron emitting electrodes comprising precipitating a thin surface layer of an alkali metal on a metal base prior to the installation of the electrodes in yan electron multiplier, intermittently controlling the thickness of the precipitated layer by meas- "thin surface layer of an alkali metal on a metal base prior to the installation of the electrodes in an electron multiplier, installing the electrodes having said thin layer thereon in said electron multiplier, and then subjecting the electrodes to a glow discharge in the presence of a rare gas until any oxidation of said thin layer has been reduced.

5. A method for producing secondary electron emitting electrodes comprising precipitating a thin surface layer of anpalkali metal on a metal base priorto the installation of the electrodes in an electron multiplier, installing the electrodes having said thin layer thereon in said electron multiplier, and then subjecting the electrodes to a -glow discharge in the presence of a chemically inactive gas until any oxidation of said thin layer has been reduced.

6. A method for producing secondary electron emitting electrodes comprising precipitating a thin surface layer of an alkali metal on a metal base prior to the installation of the electrodes in an electron multiplier, installing the electrodes having said thin layer thereon in said electron multiplier, then subjecting the electrodes to a glow discharge until any oxidation of said thin layer has been reduced, and controlling the effect of the glow discharge by measuringv intermittently the sensitiveness of the secondary electron emission.

PAUL GRLICH. 

